The present disclosure relates to a wing. More specifically, aspects of the invention relates to a variable shaped wing movable incrementally between a neutral configuration and a deformed configuration, wherein the wing takes a reflexed camber aerofoil section shape in the deformed configuration.
The camber of an aerofoil or wing can be defined by a mean camber line, which is the curve that is halfway between the upper and lower surfaces of the aerofoil and passing through the aerofoil's leading and trailing edges, that is forward most and rear most points respectively. An aerofoil where the camber line reverses curvature direction near the trailing edge is called a reflexed camber aerofoil.
Reflex aerofoils are the type of section used in flying wing aircraft due to the inherent tendency of the shape to induce a rotational moment to the trailing edge of the wing, so as to replace the more traditional tail plane surface that is used to maintain the wing at a stable positive angle of attack. This wing section, when used in a flying wing or blended wing/fuselage configuration, has considerable advantages in aircraft design where the omission of the tail boom and tail plane reduces drag by a large factor and improves efficiency, fuel consumption and performance.
In general, wings having variable shape aerofoil sections for the purpose of varying lift characteristics are known and have been achieved in the past in many difference ways. One way is by using a fabric to form the skin of the aerofoil as, for example, disclosed by LATHAM, U.S. Pat. No. 4,530,301. Fabrics are inherently stretchable, accommodating the change in overall perimeter length as the aerofoil is manipulated between differently shaped aerofoil sections. The change in aerofoil section perimeter length does not enable the aerofoil to be deflect into a reflexed camber aerofoil section. The inability of fabric to resist and transmit compressive loads further prevents this type of aerofoil to be deflected into a reflexed camber aerofoil section. The fabric of this type of aerofoil is generally pulled taut over fixed leading and/or trailing edge formations, such as leading and/or trailing edge guide wires, further restricting the aerofoil from taking a reflexed camber aerofoil section.
Another type of aerofoil employs a sliding joint along the aerofoil section that takes up a change in the overall perimeter length of the aerofoil section as it is moved between its various aerofoil section shapes. GRANT, U.S. Pat. No. 2,022,806 teaches of an aerofoil having a sliding joint positioned at a leading edge or at any position along the underside of the aerofoil. Another example is FERGUSON, U.S. Pat. No. 4,624,203, disclosing a wing sail having a variable aerofoil section with a sliding joint positioned at a trailing edge thereof. With the sliding joints enabling length changes in the overall perimeter of these types of aerofoils, the ability to deflect the trailing edge into a reflexed camber aerofoil section is not possible.
EP 1,535,835 issued to RAUTIO et al also teaches of a sliding joint type aerofoil. The significance of this sliding joint type aerofoil is that it appears to have the ability of taking a very slight reflexed camber aerofoil section shape. However, the hinge points about which the nose of this aerofoil is deformable with respect to the rest of the aerofoil forms an indent along the aerofoil section, not conducive to forming a smooth, continuous and efficiently shaped aerofoil section. Furthermore, with this aerofoil not being closed, it is possible for dirt to collect within the hinges and the sliding joint, which is detrimental to the safe and reliable operation of the aerofoil, particularly in aviation applications.
Other types of variable aerofoils having the ability of producing an aerofoil section having a S-shaped camber line normally associated with reflexed camber aerofoil sections will be referred to generally in this description as spine-supported flexing aerofoils and rotating cam aerofoils.
An example of a spine-supported flexing aerofoil is disclosed by BEAUCHCHAMP el al, U.S. Pat. No. 5,367,970. This patent document teaches of an aerofoil fin structure having nose and tail segments supported on resilient spines cantilevered from opposite ends of a central segment. Cables extending between the nose and tail segments and the central segment can be tensioned to cause the nose and tail segments to move up and down independently of one another. A skin envelopes the aerofoil fin structure, and is manipulated thereby to produce an aerofoil section shape having an S-shaped camber line.
MUELLER, CZ 300,728, discloses an example of a rotating cam aerofoil comprising a structure having a nose segment and a tail segment rotatably mounted to either end of a central segment such that the nose and tail segments are rotatable about a camber line axis passing between the leading and trailing edges of the aerofoil and with respect to the central segment. In this manner the nose is rotatable upwards and the tail is rotatable downwards (or vice versa) independently of one another. A skin encasing the rotating cams rides on the cams and is actuated to form an aerofoil section with an S-shaped camber line.
It is believed that the skins of the abovementioned spine-supported flexing aerofoils and rotating cam aerofoils may in fact have to be made from a stretchable material or tethered to the internal structure such that the skin conforms to the shape of the internal structure to take the various aerofoil section shapes. Furthermore, separate nose, central and tail segments, together with the necessary actuating mechanisms, are needed to create the at least two points of inflection required to form the S-shaped camber line of these aerofoils.
It will be appreciated that the components required for creating the necessary points of inflection make these aerofoils heavier than required, complex and unnecessarily expensive to produce.
Yet another type of variable aerofoil is an articulated type as disclosed by RINN et al, U.S. Pat. No. 6,045,096. The aerofoil includes a skin pulled over an internal articulated structure, which structure enables the tail to “wag” across the neutral camber line and in so doing, vary the aerofoil section of the aerofoil.
Due to the tail portion of the skin, or a significant part thereof, being directly supported on the internal articulated structure, the tail itself is unable to deflect between convex and concave shapes as required to form a reflexed camber aerofoil section. Many of these types of aerofoils also have a fixed, non-movable leading edge, which is not conducive to variably forming efficient aerofoil sections. Similarly, as is the case with spine-supported flexing aerofoils and the rotating cam aerofoils, the articulated aerofoils are also heavier than required, complex and unnecessarily expensive to produce.
CAMPANILE et al, U.S. Pat. No. 6,010,098 discloses an aerofoil having a deformable self-supported rigid outer skin shell, or a rigid skin supported over deformable external girdles. Although this aerofoil appears to be capable of providing a variety of smooth aerofoil sections, the aerofoil is overly complicated requiring multiple struts to deform the outer skin. Furthermore, there is not mention of the outer skin being resilient and inherently returnable to a neutral position.
Further shortcomings of this invention include the positioning of the supporting structure, which fixes at least two points on the underside of the aerofoil to an external structure such as an aeroplane and the asymmetrical neutral shape of the aerofoil section. Both of the aforementioned features lead to the ability of the aerofoil to take an aerofoil section shape having a wavy-like camber, but not a pure reflexed camber aerofoil section shape. As a result, the trailing edge of the aerofoil is incapable of taking a concave shape on the upper side thereof (i.e. always a convex shape), forcing airflow off the upper side to always be directed from the trailing edge operatively downwardly.